Specific 5-HT receptor sites include 5-HT.sub.1A, 5-HT.sub.1B, 5-HT.sub.1D, 5-HT.sub.2A, 5-HT.sub.2B 5-HT.sub.2C, 5-HT.sub.3, and 5-HT.sub.4 sites. Each of these receptors mediates certain physiological effects. See Leonard, B. E., International Clinical Psychopharmacology, 7:13-21 (1992). It is particularly desired to obtain compounds which selectively mediate certain of the 5-HT receptor sites. The present invention provides new compounds which are particularly useful for modulating a 5-HT.sub.2B receptor with surprising selectivity and potency.